It would be desirable to employ copper-containing materials in semiconductor devices. Copper has conductive properties that are superior to those of many of the conductive materials presently utilized in semiconductor devices. Unfortunately, copper has a drawback associated with it that it cannot generally be placed against oxide-comprising insulative materials (such as, for example, silicon dioxide). If copper-containing materials are placed adjacent oxide-comprising insulative materials, oxygen can diffuse into the copper-containing material and react to reduce conductivity of the material. Also, copper can diffuse into the oxide-containing material to reduce the insulative properties of the oxide-containing material. Additionally, copper can diffuse through oxide insulative material to device regions and cause degradation of device (e.g., transistor) performance. The problems associated with copper are occasionally addressed by providing nitride-containing barrier layers adjacent the copper-containing materials, but such can result in problems associated with parasitic capacitance, as illustrated in FIG. 1. Specifically, FIG. 1 illustrates a fragment of a prior art integrated circuit, and illustrates regions where parasitic capacitance can occur.
The structure of FIG. 1 comprises a substrate 10, and transistor gates 12 and 14 overlying substrate 10. Substrate 10 can comprise, for example, monocrystalline silicon lightly doped with a p-type background conductivity-enhancing dopant. To aid in interpretation of the claims that follow, the term “semiconductive substrate” is defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
Transistor gates 12 and 14 can comprise conventional constructions such as overlying layers of gate oxide, polysilicon and silicide. Insulative spacers 16 are formed adjacent transistor gates 12 and 14, and conductively doped diffusion regions 18, 20 and 22 are formed within substrate 10 and proximate gates 12 and 14. Also, isolation regions 24 (shown as shallow trench isolation regions) are formed within substrate 10 and electrically isolate diffusion regions 18 and 22 from other circuitry (not shown) provided within and over substrate 10.
An insulative material 26 extends over substrate 10, and over transistor gates 12 and 14. A conductive plug 28 extends through insulative material 26 to contact conductive diffusion region 20. Conductive plug 28 can comprise, for example, conductively doped polysilicon. Insulative material 26 can comprise, for example, silicon dioxide or borophosphosilicate glass (BPSG). Insulative material 26 and plug 28 together comprise a planarized upper surface 29. Planarized surface 29 can be formed by, for example, chemical-mechanical polishing.
A second insulative material 30 is formed over insulative material 26 and on planarized upper surface 29. Second insulative material 30 can comprise, for example, borophosphosilicate glass or silicon dioxide. A conductive material 32 is formed within an opening in insulative material 30 and over conductive plug 28. Conductive material 32 comprises copper. The copper can be, for example, in the form of elemental copper, or in the form of an alloy. Conductive material 32 is separated from conductive plug 28 by an intervening barrier layer 34. Barrier layer 34 typically comprises a conductive material, such as titanium nitride (TiN) or tantalum nitride (TaN), and is provided to prevent out-diffusion of copper from conductive material 32 into either insulative material 26 or the polysilicon of conductive plug 28. Barrier layer 34 can also prevent diffusion of silicon or oxygen from layers 26, 28 and 30 into the copper of conductive material 32. It is desired to prevent diffusion of oxygen to the copper of material 32, as such oxygen could otherwise reduce conductance of material 32. Also, it is desired to prevent copper diffusion from material 32 into insulative layer 26, as such copper could reduce the insulative properties of the material of layer 26. Additionally, diffusion through layer 26 and into one or more of regions 18, 20 and 22 can reduce the performance of transistor devices.
A second conductive material 36 is provided over insulative material 26 and spaced from first conductive material 32. Second conductive material 36 can comprise, for example, conductively doped polysilicon or a conductive metal, or a combination of two or more conductive materials (such as copper and TiN). Second conductive material 36 is spaced from first conductive material 32 by an intervening region of insulative material 30 and barrier layer 34.
Insulative material 30, barrier layer 34, first conductive material 32 and second conductive material 36 share a common planarized upper surface 37. Planarized upper surface 37 can be formed by, for example, chemical-mechanical polishing.
An insulative barrier layer 38 is provided over planarized upper surface 37. Insulative barrier layer 38 can comprise, for example, silicon nitride.
An insulative layer 40 is provided over insulative barrier layer 38. Insulative layer 40 can comprise, for example, silicon dioxide or BPSG. Insulative barrier layer 38 inhibits diffusion of copper from first conductive material 32 into insulative layer 40, and inhibits diffusion of oxygen from insulative layer 40 into first conductive material 32.
Another insulative layer 42 is provided over insulative layer 40, and a third conductive material 44 is provided within insulative material 42 and over first conductive material 32. Insulative material 42 can comprise, for example, BPSG or silicon dioxide, and third conductive material 44 can comprise, for example, conductively doped polysilicon or a metal, or a combination of two or more conductive materials (such as copper and TiN).
Conductive materials 32, 36 and 44 can be conductive interconnects between electrical devices, or portions of electrical devices. The function of materials 32, 36 and 44 within a semiconductor circuit is not germane to this discussion. Instead, it is the orientation of conductive materials 32, 36 and 44 relative to one another that is of interest to the present discussion. Specifically, each of materials 32, 36 and 44 is separated from the other materials by intervening insulative (or dielectric) materials. Accordingly, parasitic capacitance can occur between the conductive materials 32, 36 and 44. A method of reducing the parasitic capacitance is to utilize insulative materials that have relatively low dielectric constants (“k”). For instance, as silicon dioxide has a lower dielectric constant that silicon nitride, it is generally preferable to utilize silicon dioxide between adjacent conductive components, rather than silicon nitride. However, as discussed previously, copper-containing materials are preferably not provided against silicon dioxide due to diffusion problems that can occur. Accordingly, when copper is utilized as a conductive material in a structure, it must generally be spaced from silicon dioxide-comprising insulative materials to prevent diffusion of oxygen into the copper structure, as well as to prevent diffusion of copper into the oxygen-comprising insulative material. Accordingly, the copper materials are generally surrounded by nitride-comprising materials (such as the shown barrier layers 34 and 38) to prevent diffusion from the copper materials, or into the copper materials. Unfortunately, this creates the disadvantage of having relatively high dielectric constant nitride materials (for example, the material of layer 38) separating conductive materials. Accordingly, the requirement of nitride-comprising barrier layers can take away some of the fundamental advantage of utilizing copper-comprising materials in integrated circuit constructions.